A) Field of the Invention
This invention relates to a capacitance sensor and its manufacturing method.
B) Description of the Related Art
Conventionally, a capacitance sensor used as a pressure sensor and a microphone is well-known. For example, refer to JP 2002-518913. The capacitance sensor has a diaphragm and a plate that function as opposing electrodes of the condenser, converts displacement of the diaphragm corresponding to power added on the diaphragm into an electric signal and outputs the signal. That is, the capacitance sensor is used in a condition that a bias voltage is imposed on and change in capacitance by displacement of the diaphragm is output as voltage change from the capacitance sensor.
By the way, when the diaphragm and the plate are formed by well known doped polycrystalline silicon films, large stress in a direction of stretching is accumulated on the films. However; increase in displacement of the diaphragm corresponding to the power can increase sensitivity, so it is preferable that tension decided by the stress of the diaphragm is small. On the other hand, it is preferable that rigidity of the plate is high in order not to stick the diaphragm to the plate by the electrostatic attraction. The stress of the plate is one of factors to decide the rigidity of the plate.